Piezoelectric materials are well known for their tendency to generate or alter a voltage when subjected to mechanical stress. This property enables varying use of such materials, for example as a crystal in a microphone to generate electrical signals responsive to sound, or in a pressure gauge. One such use is shown in U.S. Pat. No. 4,445,384 to Royer granted May 1, 1984, assigned to the assignee of this application. Royer shows inner and outer ring electrodes 22 and 24 formed in a dielectric layer 32 which separates the electrodes from a layer of piezoelectric material, for example zinc oxide. A uniform pressure applied to layer 34 will induce piezoelectric polarizations in capacitors C1 and C2 between the piezoelectric material and electrodes 22 and 24, respectively.
Another use for piezoelectric material is in hydrophones used to detect sound transmitted through water by converting the acoustic energy into electrical energy. The hydrophone typically includes a rigid, thin walled tube of piezoelectric ceramic material, closed at each end by a rigid metal end cap. Such hydrophones must be handled with care due to the fragility of the walls. They also are quite limited in operating depth, or must be pressure compensated when used in deep water. Moreover, due to their typically small size, many such hydrophones would be required to form a large, single transducer, with individual hydrophones distributed about the transducer periphery. Such arrangement, while effective, would be prohibitively expensive.
Therefore, it is an object of the present invention to provide a large, inexpensive underwater acoustical transducer.
Another object is to provide a transducer sufficiently rugged to withstand rough handling and use in water of virtually any depth, and without pressure compensation.
Yet another object of the invention is to provide an underwater transducer that is elastically deformable from a normal, deployment configuration to a relatively compact storage configuration, retaining the tendency to rapidly assume the deployment configuration responsive to a slight disturbance.